The present invention relates to the manufacture of wood products, and more specifically to the manufacture of elongate dimension lumber such as two-by-four studs from a lumber cant having two substantially flat, mutually parallel surfaces, two irregular longitudinal wanes and a generally trapezoidal cross section.
Increasing use of secondary growth timber, with its smaller diameters and more irregular tapers than timber from mature virgin forests, has increased the difficulties of reducing somewhat cylindrical logs into dimension lumber. Simultaneously, increasing demand for lumber products, long-term growth requirements, and decreasing harvesting areas dictate the avoidance of unnecessary waste. Automated processing systems have heretofore sought to resolve these competing considerations by providing optimum cutting schemes to obtain optimum yield from each log and thereby reduce the amount of wood waste.
Conventional lumber manufacturing is generally achieved in a multi-stage process. Initially, the log undergoes a series of slab cuts resulting in a log having two substantially flat, mutually parallel faces and a reduced taper. The fist stage is typically completed by a series of longitudinal cuts parallel to the faces and transversely spaced by combinations of dimensions corresponding to the numerical "1, 2 and 4" inches used in the sizing of dimension lumber. The cants resulting from these cuts have two substantially flat, mutually parallel surfaces, two irregular longitudinal wanes and a generally trapezoidal cross section.
Longitudinal edge trimming removes the cant's irregular longitudinal wanes thereby forming rectangular dimension lumber. Since the cant typically has one flat surface which is generally narrower than the opposing surface, and since the longitudinal boundaries of both flat surfaces are irregular, derivation of the largest rectangular dimension lumber contained therein requires two longitudinal edging cuts, perpendicular to the flat surfaces and transversely spaced according to the nominal width of the lumber as limited by the narrowest width dimension of the flat surfaces. Accordingly, edge trimming requires a determination both of the narrowest width of the flat surfaces and of the orientation of that width relative to the wanes.
It has been recognized for some time that an electronic computer can calculate the most advantageous orientation and spacing of the edging cuts, but this requires an imputting device which can translate cant configuration into computer-compatible signals. Scanning cants by means of reflected light and light sensors is a well known approach to such signal translations. However, no system utilizing such apparatus has heretofore been entirely satisfactory due to inaccuracies resulting from unpredictable reflectivity characteristics of different cants and ambient light fluctuations.
In Sanglert U.S. Pat. No. 3,886,372 a cant is longitudinally advanced upon a first conveyor to a point where its narrowest flat surface is exposed to a reflective scanner. The configuration of the cant is then determined by relecting light from its narrowest flat surface to an array of light sensors. Variations in light intensity, caused by reflective qualities of flat and angular surfaces, are sensed by the light detectors and correspond to the four respective flat surface boundaries defined by the cant's wanes. A computer uses the scan data to orient the cant by using a second opposing conveyor to move the cant at right angles relative to the first conveyor, and to transversely space a pair of edge trimming saws. Thereafter, the cant is longitudinally advanced on the first conveyor to the saws.
In Maxey U.S. Pat. No. 3,890,509 a cant is transversely advanced on a fast conveyor to a slow conveyor where the cant engages indexing lugs and thereafter advances to a position where its narrowest flat surface is exposed to a reflective scanner. Scan data is used by a computer to transversely space cant chipper saws and to position a pair of adjustable stops relative to the position of the saws. Once scanning is completed, the cant is transversely advanced until it engages the stops thereby being oriented relative to the saws. Thereafter, a third conveyor longitudinally advances the cant to the saws.
In Sanglert U.S. Pat. No. 3,963,938 a cant is transversely advanced by a plurality of belts to a scanning station, where it engages reference stops with its narrowest flat surface exposed to a reflective scanner. Scan data is used to adjust a plurality of orienting stops and to transversely space cant chipper saws. Thereafter, the cant is transversely advanced by the belts until it engages and orienting stops, at which time the reference stops are released, the belts deactivated, and a plurality of rollers are activated to longitudinally advance the cant to the saws.
In Kohlberg U.S. Pat. No. 3,970,128 an improved relective cant scanner an orientation system incorporating features of Sanglert U.S. Pat. No. 3,963,938 is set forth and includes a device for selectively moving the reference stops to engage the cant at optimum positions. Finally, Dahlstrom et al U.S. Pat. No. 3,983,403 presents yet another reflective type scanner and indexing orienting apparatus.
A common difficulty present in these conventional scanners is that they determine cant boundaries by directing light upon the narrowest flat face and reflecting light therefrom to light sensors and, hence, the cant must be placed with its narrowest flat side facing the light source(s). However, mechanical transfer equipment occasionally places the cants in an inverted orientation and thereby necessitates interruptions in edge trimming operations to manually turn the cant to an upright orientation.
A further deficiency of the devices described is that reflective scanning accuracy depends on sensor light sensitivity and cant surface reflectivity. Practical lumbering operations, however, produce cants varying in surface coloration from black to white and including highly reflective sap and, hence, reflecting widely disparate quanta of light therefrom. Also, lumbering operations produce cants having wane edges which form acute angles varying from 10.degree. to 90.degree. relative to the flat surfaces and, hence, reflect light patterns which vary widely in their delineation of the cant's wane edges. These factors make scanner illumination levels and detector sensitivity critical. Accordingly, frequent and extensive calibrations using a wide variety of test objects are required.
Further, high wattage light sources are required and, hence, the process consumes considerable energy. Dahlstrom et al eliminates the need for high intensity lamps but does so by incorporating overly complex mechanical apparatus to elevate the cant to a position in close association with the scanner. More importantly, the low reflective quality of dark wood necessitates high response sensors having a low signal-to-noise rejection capacity. Accordingly, conventional cant scanners are quite sensitive to fluctuations in the ambient light. Maxey decreases the number of erroneous responses to ambient light fluctuations by shielding his detectors with baffles. The detectors, however, receive light from a plurality of acute angles and, as a consequence, the baffles cannot completely shield the detectors.
Yet another difficulty is that conventional cant scanners do not measure cant height. Prior cant operations were based upon the assumption that satisfactory yield could be achieved by producing only two and four inch cants and, hence, devices such as the one suggested by Maxey which differentiate between two and four inch cants have heretofore provided satisfactory results. As described earlier, optimum yield often dictates the generation of more than two cant heights, and optimum edge trimming requires cant and saw orientations which are based in part upon the cant height.
Several measuring devices of the so-called "broken beam" have also been presented for detecting log diameter and taper by advancing logs between the light source and the sensors to momentarily cause "light" and "no light" conditions which correspond to their dimensions. Denton U.S. Pat. No. 3,806,253; Sherman 3,513,321 and Chasson 3,897,156 are particularly relevant in this regard. Diameter measuring methods, however, are unsuitable for cant scanning operations in part because they do not involve maintenance of log orientation. In fact, known log processing methods require that the log be rotated after diameter scanning in order to present optimum sawing faces to the slab trimming saws. Equally important, Chasson requires a linear array sensing light from a wide range of angles, and Denton requires a 90.degree. angular separation between his sensors, in order to compensate for the placement of the log in its V-block and for its eccentricity. Conversely, broken beam cant scanning, as described hereafter, requires that the angular separation between sensors be less than the acute angles formed by the longitudinal cant wanes with respect to the flat cant surfaces. Accordingly, the methodology disclosed by Chasson and Denton cannot supply the boundary information that is required for cant edge trimming operations.
What is needed therefore, and what the present invention provides, is a method for: (1) determining both the narrowest width of a cant's flat surfaces and the orientation of the boundaries of the narrowest width portion, (2) for orienting and transversely spacing cant trimming saws dependent upon such width, boundaries and desired lumber dimensions, and (3) for longitudinally advancing the cant to the saws in proper orientation therewith, such method being indifferent to cant coloration, or reflectivity, fluctuations in the ambient light and the upright or inverted orientation of the cant's narrowest flat surface relative to the scanner.